This invention relates generally to the field of transportation of vehicles by rail, ship, truck and, more particularly, to the transportation of wheeled vehicle by air. For all modes of transport it is necessary to fasten (tie-down) the vehicles to some structure to hold them in place, out of contact with each other and surrounding structure, under the inertial loads and associated displacements caused by various accelerations experienced by the transport. The accelerations include starting, stopping, turning and all manner of bumping, jolting, and the like.
Aircraft cargo is usually "containerized" (put in a container) or "palletized" (fastened to a pallet) to facilitate handling the cargo with standardized equipment and to facilitate securing the cargo in the airplane using the standardized cargo handling and restraint equipment built into the airplane.
One of the prime reasons for transporting vehicles by air is the economic benefit achieved by the shortening of time of transportation, which in turn allows keeping smaller inventories of vehicles at distribution centers and dealers. To be consistent with the saving of time by using air transportation, it is necessary to load and unload the vehicles expeditiously, taking best possible advantages of the time savings afforded by automation of the loading and unloading. Much of the equipment for such automation could be adapted from equipment developed for modes other than air transportation. However, it is particularly important to air transportation that the equipment be light, compact, and require a minimum of access space around the vehicles. Tie-down equipment developed for other transport modes is not readily adaptable to these requirements and to rapidly and automatically tying vehicles down to pallets or to the bases of containers.
The Vehicle Positioning and Restraint Apparatus of U.S. Pat. No. 3,738,481 shows apparatus which is specifically adapted to rapid automatic tie-down of wheeled vehicles to the floor or base of a carrier, specifically a shipping container. The apparatus comprises three rails attached to the floor of the container and three devices which connect the vehicle to the rails and restrain the vehicle against up and down, lateral and longitudinal motion with respect to the rails and container. The restraints are rigid with the exception of some resilience longitudinally. Also, as the vehicle is installed its suspension system springs are compressed, resulting in a tension preloading in the tie-down apparatus. In such a situation any upward vertical acceleration of the carrier, caused by roughness of the road or rails, for example, will react with the inertia of the vehicle and tend to reduce the preload in the connection devices. Great enough accelerations will, in fact, overcome the preload and cause compression loads on the devices. Since there is no resilience in the vertical restraint, these load changes will cause unacceptable sharp, jolting loads on the vehicle, connection devices, and rails. This problem can be minimized by designing the apparatus to produce higher preloading of the tires, springs, and apparatus. However, higher preloading has the disadvantages of increasing the forces required for installing and removing the vehicle and requiring stronger, heavier apparatus. This second disadvantage is of particular concern to air transportation of vehicles.
Another facet of this prior art approach is that it requires separate sets of rails and connection fittings for each type of vehicle to be transported. This is severely disadvantageous in terms of costs for design, construction, inventorying, parts handling, and record keeping.
The apparatus in U.S. Pat. No. 3,841,235, "Wheeled Vehicle Tie-Down Device", comprising rails, cables and winches, is satisfactorily adjustable. However, it does not lend itself to automated use since four cables must be each attached manually to the vehicle after it has been placed on the support for shipment.
In this apparatus also the tie-down involves preload tension in the tie-down cables and compression of the vehicles' suspension system springs and tires. Since the cables are angularly situated between the vehicle and rails, vertical and horizontal or combined inertial loads on the vehicle, due to roadway roughness and carrier operation, which exceed the preload will cause the cables to go slack and then snap taut when the inertial loads are relieved. The resulting shock loads are undesirable and may require the apparatus to be stronger and heavier than desirable for air transport purposes. In addition, costly space is required around the vehicle for access for attaching and/or adjusting the apparatus. Also, each pallet or floor must be equipped with "active" apparatus, such as winches. This tends to increase costs and weight.
United States Pat. No. 3,140,850, "Vehicle Tie-Down Apparatus"; 2,024,444, "Car Loading Device"; and 3,566,804, "Jack for Adjusting Cargo Hold-Down Apparatus" all show apparatus similar in principle to that of U.S. Pat. No. 3,841,235, discussed above, and the discussion applies to these three patents as well, with the exception that U.S. Pat. No. 2,024,444 shows a spring loaded turnbuckle in each tie-down element (chain). Since these elements are angled at approximately 45.degree. to vertical, the springs provide for resilience both vertically and longitudinally. However, the operation is fully manual, including hook-up of the elements and adjustment, and, as stated, springs are required in each tie-down element. For air transport of vehicles this apparatus is undesirably complex and time consuming. It would also require considerable space around the vehicles for access for attachment and adjustment of the apparatus.